1. Field of the Invention
This invention relates to an optical element module having a coil in a bias circuit for supplying power.
2. Description of the Related Art
FIG. 28 is a top view showing a structural example of a conventional optical element module. In FIG. 28, reference numerals 1, 2, and 3 respectively designate a light emitting element for converting an electric signal and an optical signal, a light emitting element carrier as a substrate for mounting this light emitting element 1 and manufactured by aluminum nitride, and a light receiving element for monitoring a rear face output from the light emitting element 1. Reference numerals 4, 5, and 6 respectively designate a light receiving element carrier for mounting this light receiving element 3, a filter, and a filter substrate for mounting this filter 5. Reference numerals 9, 11, and 13 respectively designate a package for airtightly sealing the light emitting element 1, etc., a feed-through having a coplanar or a microstrip line, etc. for electrically conducting the interior and the exterior of this package 9, and an electrode for high frequency arranged in this feed-through 11 and supplying an RF signal to the light emitting element 1. Reference numerals 15, and 17 respectively designate an electrode for bias arranged in the feed-through 11 and supplying a bias electric current from an unillustrated power source to the light emitting element 1, and an optical fiber for transmitting the optical signal.
FIG. 29 is a top view of a main portion of the conventional optical element module shown in FIG. 28. FIG. 30 is a side view of the main portion shown in FIG. 29. In these figures, reference numerals 19, 20, and 5a respectively designate a base carrier for placing the light emitting element carrier 2 and the light receiving element carrier 4, a pattern formed on the light emitting element carrier 2, and an air-core coil as a central portion of the filter 5. Reference numerals 21a and 21b designate connecting portions extending from one end and the other end of this air-core coil 5a. The filter 5 is constructed by this air-core coil 5a and the connecting portions 21a and 21b. Reference numerals 22a and 22b respectively designate solder joining portions for soldering and joining the connecting portions 21a and 21b to the filter substrate 6. Reference numeral 23a designates a bonding wire for making an electrical connection between the electrode 15 for bias and the solder joining portion 22a. Reference numeral 23b designates a bonding wire for making an electrical connection between the solder joining portion 22b and the pattern 20. Reference numeral 23c designates a bonding wire for making an electrical connection between the pattern 20 and the light emitting element 1. Reference numeral 23d designates a bonding wire for making an electrical connection between the pattern 20 and the electrode for high frequency.
The conventional optical element module is constructed as mentioned above. An RF signal transmitted from an unillustrated driver IC is inputted to the light emitting element 1 via the electrode 13 for high frequency, the bonding wire 23d, the pattern 20 and the bonding wire 23c. A direct current (DC) for supplying the bias electric current from the power source to the light emitting element 1 is inputted to the light emitting element 1 via the electrode 15 for bias, the bonding wire 23a, the solder joining portion 22a, the connecting portion 21a, the air-core coil 5a, the connecting portion 21b, the solder joining portion 22b, the bonding wire 23b, the pattern 20 and the bonding wire 23c. 
Namely, a bias circuit for supplying power is generally arranged in the optical element module in addition to a circuit for supplying the RF signal. The air-core coil 5a is a noise countermeasure part used in this bias circuit, and functions as a filter for preventing the RF signal from being transmitted to the bias circuit. The air-core coil 5a is widely used as a part for the bias circuit for the following reasons, etc. Namely, (1) compactness can be realized by a precise winding technique, (2) the electric current flowing through the air-core coil 5a can be increased since the air-core coil 5a has low direct current resistance, and (3) the RF signal can be prevented in a wide band since parasitic capacity is small and self resonance frequency is high.
On the other hand, a high speed operation of the optical element module is required to cope with an increase in transmission capacity. Recently, the optical element module of 10 Gbps or more is required instead of the conventional optical element module of 2.5 Gbps.
Here, when the length of a line path (the total of lengths of the connecting portion 21b, the solder joining portion 22b, the bonding wire 23b, the pattern 20 and the bonding wire 23c) between the light emitting element 1 and the bias circuit (the air-core coil 5a in this case) is longer than xc2xc of an upper limit frequency wavelength in a passing band, the resonance frequency of the line path itself between the light emitting element 1 and the bias circuit lies within this passing band. Therefore, the passing band is limited by this resonance. It is necessary to set the line path length between the light emitting element 1 and one end of the air-core coil 5a to about 1 mm or less so as to cope with the recent high speed of 10 Gbps or more.
In the conventional optical element module, as mentioned above, the filter substrate 6 mounting the air-core coil 5a thereto is mounted in the vicinity of the light emitting element 1, and the light emitting element 1 and the air-core coil 5a are electrically connected to each other by the bonding wires 23b, 23c, etc. Therefore, a problem exists in that it is difficult to set the line path length between the light emitting element 1 and the air-core coil 5a to about 1 mm or less, and no preferable high frequency characteristics are obtained.
This invention is made to solve the above problem, and an object of this invention is to provide an optical element module able to obtain preferable high frequency characteristics by shortening the line path length between the light emitting element 1 and the air-core coil 5a. 
An optical element module in this invention comprises alight emitting element; and a filter portion used in one portion of a bias circuit for supplying a bias electric current from a power source to this light emitting element; wherein this filter portion has a coil portion and a first connecting portion extending from one end of this coil portion; and the first connecting portion directly connects the coil portion and the light emitting element without electrically joining the first connecting portion to any substrate on the way.
In the optical element module in this invention, the coil portion and the light emitting element are connected to each other by thermocompression-bonding a one-side end portion of the first connecting portion to the light emitting element.
In the optical element module in this invention, the light emitting element has a metallic electrode on its surface, and a one-side end portion of the first connecting portion is constructed by forming a metallic film on a lead wire, and the coil portion and the light emitting element are connected to each other by joining the one-side end portion having the metallic film to the metallic electrode.
In the optical element module in this invention, the light emitting element has a metallic electrode on its surface, and the coil portion and the light emitting element are connected to each other by fixing a one-side end portion of the first connecting portion to this metallic electrode by a bump.
In the optical element module in this invention, the one-side end portion of the first connecting portion is constructed by forming a metallic film on a lead wire.
In the optical element module in this invention, the first connecting portion has a length shorter than xc2xc of a wavelength corresponding to an upper limit frequency of a high frequency signal supplied to the light emitting element.
In the optical element module in this invention, the first connecting portion has a length of 1 mm or less.
In the optical element module in this invention, an optical element module comprises a package; a feed-through for electrically conducting the interior and the exterior of this package, and having a shelf portion projected to the interior; a light emitting element included within the package; and a filter portion used in one portion of a bias circuit for supplying a bias electric current from a power source to the light emitting element; wherein this filter portion has a coil portion and a first connecting portion extending from one end of this coil portion, and also has a second connecting portion extending from the other end of the coil portion; the first connecting portion directly connects the coil portion and the light emitting element without electrically joining the first connecting portion to any substrate on the way; and the second connecting portion directly connects the other end of the coil portion and the shelf portion of the feed-through without electrically joining the second connecting portion to any substrate on the way.
In the optical element module in this invention, a filter portion for low frequency is arranged in the shelf portion of the feed-through, and is electrically connected in series to the coil through the second connecting portion.
In the optical element module in this invention, the light emitting element has a gold electrode on its surface, and the filter portion is constructed by one copper wire, and an insulating film is formed on the coil portion, and a gold film is formed on a one-side end portion of the first connecting portion, and the coil portion and the light emitting element are connected to each other by joining the one-side end portion having this gold film to the gold electrode of the light emitting element.
In the optical element module in this invention, an optical element module comprises a light emitting element; a substrate mounting this light emitting element thereto; and a filter portion used in one portion of a bias circuit for supplying a bias electric current from a power source to the light emitting element; wherein this filter portion has a coil portion and a first connecting portion extending from one end of this coil portion; and the first connecting portion directly connects the coil portion and the substrate mounting the light emitting element thereto without electrically joining the first connecting portion to any substrate on the way.
In the optical element module in this invention, the coil portion and the substrate mounting the light emitting element thereto are connected to each other by thermocompression-bonding a one-side end portion of the first connecting portion to the substrate mounting the light emitting element thereto.
In the optical element module in this invention, the substrate mounting the light emitting element thereto has a metallic pattern on its surface, and a one-side end portion of the first connecting portion is constructed by forming a metallic film on a lead wire, and the coil portion and the substrate mounting the light emitting element thereto are connected to each other by joining the one-side end portion having the metallic film to the metallic pattern.
In the optical element module in this invention, the substrate mounting the light emitting element thereto has a metallic pattern on its surface, and the coil portion and the substrate mounting the light emitting element thereto are connected to each other by fixing a one-side end portion of the first connecting portion to this metallic pattern by a bump.
In the optical element module in this invention, the one-side end portion of the first connecting portion is constructed by forming a metallic film on a lead wire.
In the optical element module in this invention, the length of a line path from one end of the coil portion to the light emitting element is shorter than xc2xc of a wavelength corresponding to an upper limit frequency of a high frequency signal supplied to the light emitting element.
In the optical element module in this invention, the length of a line path from one end of the coil portion to the light emitting element is set to 1 mm or less.
In the optical element module in this invention, an optical element module comprises a package; a feed-through for electrically conducting the interior and the exterior of this package, and having a shelf portion projected to the interior; a light emitting element included within the package; a substrate mounting this light emitting element thereto; and a filter portion used in one portion of a bias circuit for supplying a bias electric current from a power source to the light emitting element; wherein this filter portion has a coil portion and a first connecting portion extending from one end of this coil portion, and also has a second connecting portion extending from the other end of the coil portion; the first connecting portion directly connects the coil portion and the substrate mounting the light emitting element thereto without electrically joining the first connecting portion to any substrate on the way; and the second connecting portion directly connects the other end of the coil portion and the shelf portion of the feed-through without electrically joining the second connecting portion to any substrate on the way.
In the optical element module in this invention, a filter portion for low frequency is arranged in the shelf portion of the feed-through, and is electrically connected in series to the coil through the second connecting portion.
In the optical element module in this invention, the substrate mounting the light emitting element thereto has a gold pattern constructed by gold on its surface, and the filter portion is constructed by one copper wire, and an insulating film is formed on the coil portion, and a gold film is formed on a one-side end portion of the first connecting portion, and the coil portion and the substrate mounting the light emitting element thereto are connected to each other by joining the one-side end portion having this gold film to the gold pattern.